Americans are living longer than ever, but not as long as people in 41 other countries.

For decades, the United States has been slipping in international rankings of life expectancy, as other countries improve health care, nutrition and lifestyles.

Countries that surpass the U.S. include Japan and most of Europe, as well as Jordan, Guam and the Cayman Islands.

"Something's wrong here when one of the richest countries in the world, the one that spends the most on health care, is not able to keep up with other countries," said Dr. Christopher Murray, head of the Institute for Health Metrics and Evaluation at the University of Washington.

A baby born in the United States in 2004 will live an average of 77.9 years. That life expectancy ranks 42nd, down from 11th two decades earlier, according to international numbers provided by the Census Bureau and domestic numbers from the National Center for Health Statistics.

Andorra, a tiny country in the Pyrenees mountains between France and Spain, had the longest life expectancy, at 83.5 years, according to the Census Bureau. It was followed by Japan, Macau, San Marino and Singapore.

The shortest life expectancies were clustered in Sub-Saharan Africa, a region that has been hit hard by an epidemic of HIV and AIDS, as well as famine and civil strife. Swaziland has the shortest, at 34.1 years, followed by Zambia, Angola, Liberia and Zimbabwe.

Researchers said several factors have contributed to the United States falling behind other industrialized nations. A major one is that 45 million Americans lack health insurance, while Canada and many European countries have universal health care, they say.

But "it's not as simple as saying we don't have national health insurance," said Sam Harper, an epidemiologist at McGill University in Montreal. "It's not that easy."

Among the other factors:

• Adults in the United States have one of the highest obesity rates in the world. Nearly a third of U.S. adults 20 years and older are obese, while about two-thirds are overweight, according to the National Center for Health Statistics.

"The U.S. has the resources that allow people to get fat and lazy," said Paul Terry, an assistant professor of epidemiology at Emory University in Atlanta. "We have the luxury of choosing a bad lifestyle as opposed to having one imposed on us by hard times."

• Racial disparities. Black Americans have an average life expectancy of 73.3 years, five years shorter than white Americans.

Black American males have a life expectancy of 69.8 years, slightly longer than the averages for Iran and Syria and slightly shorter than in Nicaragua and Morocco.

• A relatively high percentage of babies born in the U.S. die before their first birthday, compared with other industrialized nations.

Forty countries, including Cuba, Taiwan and most of Europe had lower infant mortality rates than the U.S. in 2004. The U.S. rate was 6.8 deaths for every 1,000 live births. It was 13.7 for Black Americans, the same as Saudi Arabia.

"It really reflects the social conditions in which African American women grow up and have children," said Dr. Marie C. McCormick, professor of maternal and child health at the Harvard School of Public Health. "We haven't done anything to eliminate those disparities."

Another reason for the U.S. drop in the ranking is that the Census Bureau now tracks life expectancy for a lot more countries  222 in 2004  than it did in the 1980s. However, that does not explain why so many countries entered the rankings with longer life expectancies than the United States.

Murray, from the University of Washington, said improved access to health insurance could increase life expectancy. But, he predicted, the U.S. won't move up in the world rankings as long as the health care debate is limited to insurance.

Policymakers also should focus on ways to reduce cancer, heart disease and lung disease, said Murray. He advocates stepped-up efforts to reduce tobacco use, control blood pressure, reduce cholesterol and regulate blood sugar.

"Even if we focused only on those four things, we would go along way toward improving health care in the United States," Murray said. "The starting point is the recognition that the U.S. does not have the best health care system. There are still an awful lot of people who think it does."